The wheels of automobiles and other land vehicles must be properly aligned to reduce tire wear, and to provide a true, free-rolling movement over the road. Wheel alignment is typically described in terms of camber, toe, caster, turning radius, and steering-axis inclination. Caster, turning radius, and steering-axis inclination are designed-in features, and are generally not subject to adjustment after a vehicle has been manufactured. Camber and toe, however, are subject to close tolerances that are difficult to achieve during manufacture and that require adjustments over the life of a vehicle.
Camber is a measurement in angular degrees of the inward or outward tilt of a wheel as measured from a vertical plane. Camber is usually considered "positive" when the top of the wheel leans outwardly towards the side of the vehicle, and is considered "negative" when the top of the wheel leans inwardly. In other words, two wheels that are at opposite ends of a common axle have positive camber when the tops of the two wheels are further apart from each other than the bottom of the wheels.
Toe is a measurement that compares the distance between the front edges of two tires supported at opposite ends of a common axle to the distance between the rear edges of the tires. In particular, "toe-in" means the front edges of the two tires are closer together than the rear edges of the tires, and "toe-out" means the front edges are further apart than the rear edges.
Incorrect alignment of either camber or toe can lead to rapid and excessive tire wear, adverse handling of a vehicle, and rapid deterioration of the bearings supporting the misaligned wheel. Camber and toe must be optimally set at the factory after assembly of a vehicle. Moreover, camber and toe should be inspected and adjusted after operation of a vehicle over rough roads, involvement of the vehicle in an accident, and during routine maintenance checks.
U.S. Pat. No. 4,037,680, issued to one of the named inventors of this application, discloses an annular, tapered shim that is placed between the spindle of a wheel and the axle to which the wheel spindle is attached. As disclosed in the '680 patent, different shims, each having different amounts of taper, can be placed between the wheel spindle and its supporting axle to selectively adjust the camber of the wheel. Locating the point of maximum thickness at the top of the installed shim yields a camber adjustment equal to the angle of taper. The shims include a plurality of apertures such that the bolts holding the wheel spindle to the axle can be received through the shim. A somewhat similar shim is shown in U.S. Pat. No. 4,195,862. With such shims multiple bolt apertures are used to permit a single shim to fit several different types of wheel spindles, but do not appear to have been used to rotationally select the different locations for the point of maximum thickness.
U.S. Pat. No. 4,684,150 discloses an annular, tapered shim for adjusting both the camber and toe of a wheel. The shim disclosed in the '150 patent includes a plurality of bolt clearing notches along its peripheral edge so that the shim can be placed between the wheel spindle and the axle in a variety of angular positions while providing clearance through different ones of the notches for the bolts connecting the spindle to the axle. Adjustment of toe, camber, or a combination of toe and camber, can be selected by changing the angular orientation of the shim so that its point of maximum thickness is at different points between the spindle and the axle.
Other shims for adjusting camber and/or toe are known. At least one of these achieves angular adjustability by utilizing elongated slots instead of bolt clearing notches along the peripheral edge, e.g., the shim identified by Part Nos. 5501 to 5508 made by Shimco Products Inc.
While the use of shims interposed between wheel spindle and axle has proven to be an effective and economical way to adjust camber and toe, certain design tradeoffs have heretofore limited the effectiveness of most shims used to adjust a combination of camber and toe alignment. In particular, a shim should present as much contact area (bearing surface) as possible to the axle and wheel spindle mounting plates it engages. Maximum bearing surface promotes integrity of the shim and the surfaces it engages, by spreading compressive forces (from wheel fasteners and road roughness) to help prevent distortion of the shim or adjacent surfaces under pressure. It also reduces the possibility of shim slippage. A shim must also, however, present bolt clearing gaps through which the bolts connecting the axle and wheel spindle can be received. It has heretofore been considered axiomatic that, in order to enable a shim to be oriented in a number of angular positions (thereby enabling the selection of a number of combinations of camber and toe adjustment effected by the shim), a great deal of shim material that would otherwise serve as bearing surface must be removed to present multiple or elongated bolt clearing gaps. A shim that could be used to adjust multiple combinations of camber and toe, yet sacrificed less in the tradeoff between bearing surface and the size of the shim bolt clearing gaps, would be a decided advantage.